Congress appeared ready to launch an investigation into the Bush administration's warrantless domestic surveillance program last week, but an all-out White House lobbying campaign has dramatically slowed the effort and may kill it, key Republican and Democratic sources said yesterday.

The Senate intelligence committee is scheduled to vote tomorrow on a Democratic-sponsored motion to start an inquiry into the recently revealed program in which the National Security Agency eavesdrops on an undisclosed number of phone calls and e-mails involving U.S. residents without obtaining warrants from a secret court. Two committee Democrats said the panel -- made up of eight Republicans and seven Democrats -- was clearly leaning in favor of the motion last week but now is closely divided and possibly inclined against it.

They attributed the shift to last week's closed briefings given by top administration officials to the full House and Senate intelligence committees, and to private appeals to wavering GOP senators by officials, including Vice President Cheney. "It's been a full-court press," said a top Senate Republican aide who asked to speak only on background -- as did several others for this story -- because of the classified nature of the intelligence committees' work.

Lawmakers cite senators such as Olympia J. Snowe (R-Maine) to illustrate the administration's success in cooling congressional zeal for an investigation. On Dec. 20, she was among two Republicans and two Democrats who signed a letter expressing "our profound concern about recent revelations that the United States Government may have engaged in domestic electronic surveillance without appropriate legal authority." The letter urged the Senate's intelligence and judiciary committees to "jointly undertake an inquiry into the facts and law surrounding these allegations."

In an interview yesterday, Snowe said, "I'm not sure it's going to be essential or necessary" to conduct an inquiry "if we can address the legislative standpoint" that would provide oversight of the surveillance program. "We're learning a lot and we're going to learn more," she said.

She cited last week's briefings before the full House and Senate intelligence committees by Attorney General Alberto R. Gonzales and former NSA director Michael V. Hayden.

"The administration has obviously gotten the message that they need to be more forthcoming," Snowe said.

Before the New York Times disclosed the NSA program in mid-December, administration briefings regarding it were highly secret and limited to eight lawmakers: the top Republican and Democratic leader of the House and Senate, respectively, and the top Republican and Democrat on the House and Senate intelligence committees.

The White House characterized last week's closed-door briefings to the full committees as a significant concession and a sign of the administration's respect for Congress and its oversight responsibilities. Many Democrats dismissed the briefings as virtually useless, but senators said yesterday they appear to have played a big role in slowing momentum for an inquiry.

John D. Rockefeller IV (D-W.Va.), the Senate intelligence committee's vice chairman, has drafted a motion calling for a wide-ranging inquiry into the surveillance program, according to congressional sources who have seen it. Rockefeller declined to be interviewed yesterday.

Sources close to Rockefeller say he is frustrated by what he sees as heavy-handed White House efforts to dissuade Republicans from supporting his measure. They noted that Cheney conducted a Republicans-only meeting on intelligence matters in the Capitol yesterday.

Senate intelligence committee member Mike DeWine (R-Ohio) said in an interview that he supports the NSA program and would oppose a congressional investigation. He said he is drafting legislation that would "specifically authorize this program" by excluding it from the 1978 Foreign Intelligence Surveillance Act, which established a secret court to consider government requests for wiretap warrants in anti-terrorist investigations.

The administration would be required to brief regularly a small, bipartisan panel drawn from the House and Senate intelligence committees, DeWine said, and the surveillance program would require congressional reauthorization after five years to remain in place.

Snowe said she is inclined to support DeWine's plan. Sen. Chuck Hagel (R-Neb.), who also signed the Dec. 20 letter seeking an inquiry, said yesterday that the FISA law should be amended to include the NSA program and to provide for congressional oversight.

As for Rockefeller's bid, Hagel said: "If some kind of inquiry would be beneficial to getting a resolution to this issue, then sure, we should look at it. But if the inquiry is just some kind of a punitive inquiry that really is not focused on finding a way out of this, then I'm not so sure that I would support that."